Question

Counting problem (passwords)
Using six lowercase letters:
a) How many if letter a appears exactly once?
b) a at least once?
c) a no more than once?

Answer 1

I am thinking that they are following:
a) 1*25^5
b) 25^5 + 25^4 + 25^3 + 25^2 + 25^1 * 1^6 (6 a's)
c) 1*25^5 + 26^6

Am I right? Or on the right track at least?

Answer 2

the first is right

Answer 3

and the others?

Answer 4

the second is correct i believe only you left out the 1's correct

Answer 5

so like the first would be
\[1*25^5\]
second would be

\[1*1*25^4\]

Answer 6

and the last is correct